JP7247357B2 - motor controller - Google Patents

Description

This application claims priority based on Japanese Patent Application No. 2019-173390 filed on September 24, 2019. The entire contents of that application are incorporated herein by reference. This specification discloses a technique related to a motor control device.

Japanese Unexamined Patent Application Publication No. 2018-58143 (hereinafter referred to as Patent Document 1) discloses a motor drive device that drives a motor having a three-phase inverter. The three-phase inverter includes a U-phase transistor pair (transistors UH, UL), a V-phase transistor pair (transistors VH, VL), and a W-phase transistor pair (transistors WH, WL). Each transistor pair is connected to a power supply, and the transistor pairs are connected in parallel. Transistors UH, VH, WH are connected to the high voltage side and transistors UL, VL, WL are connected to the low voltage side.

In Patent Document 1, for example, when the transistor UH and the transistor VL are on, one of the transistor UH and the transistor VL (specifically, the transistor UH) is switched based on the duty ratio (hereinafter referred to as PWM control). . Further, in Patent Document 1, while the transistor UH is off, the transistor UL connected in series with the transistor UH is turned on (hereinafter referred to as complementary PWM control). In Patent Document 1, when the duty ratio exceeds the threshold (that is, when the off time of the transistor UH is short), the transistor UL is not turned on, and the transistor UL is kept off. That is, when the duty ratio exceeds the threshold value, only PWM control is performed without performing complementary PWM control.

In Patent Literature 1, by stopping complementary PWM control when the duty ratio exceeds a threshold, both U-phase transistor pairs (transistors UH and UL) are prevented from being turned on at the same time. However, when the complementary PWM control is stopped, the amount of heat generated by each transistor increases, and it becomes necessary to provide a structure, device, etc. for dealing with heat generation. If the heat generation of each transistor can be suppressed, it is possible to omit (or simplify) structures, devices, etc. for countermeasures against heat generation, which is a great advantage. This specification provides a technique for realizing a motor drive device capable of suppressing heat generation of a transistor that constitutes an inverter.

A first technique disclosed in this specification is a motor control device that drives a motor connected to an inverter. The inverter may have a plurality of switching element pairs in which an upper arm element connected to the high voltage side of the power supply and a lower arm element connected to the low voltage side of the power supply are connected in series. In this motor control device, PWM control may be performed to switch the first element, which is one of the upper arm element and the lower arm element, which is selected to be ON to energize the motor, based on the duty ratio. Further, the motor control device sets a duty command value for switching the second element so that the second element connected in series with the first element performs complementary PWM control in which the second element is turned on for a predetermined time during the off period of the first element. Complementary PWM control may be performed when the determined duty command value is equal to or less than the threshold value. Furthermore, if the determined duty command value is greater than the threshold, the first element is kept ON over a plurality of carrier cycles, and the corrected duty ratio is executed so that the first element is turned OFF longer than the first period. In addition, average PWM control is performed in which the average duty ratio in the total period of the first period and the second period is the same as the set duty ratio, and the first element is turned off in the second period. The second element may be turned on while the

The second technology disclosed in the present specification is the motor control device of the first technology, and when the corrected duty ratio is smaller than the threshold, the average PWM control is performed over the entire period in which the motor is driven, and the corrected When the duty ratio is equal to or greater than the threshold value, the average PWM control is performed until the third element, which is different from the first element among the upper arm element and the lower arm element selected to be on, is turned off, and the third element is turned off. Control may be performed with a duty ratio of 100% during the period from when the first element is turned off.

A third technique disclosed in this specification is the motor control device of the first or second technique, wherein when the modified duty ratio is set, the second period when the first period spans n carrier periods Comparing the nth corrected duty ratio with a threshold, and calculating the n+1th corrected duty ratio for the second period when the first period spans n+1 carrier periods when the nth corrected duty ratio is greater than the threshold. It may be repeated (n≧2, n is an integer).

According to the first technique, complementary PWM control can be performed even when the duty ratio of the first element is so large that conventional complementary PWM control cannot be performed. Specifically, when performing complementary PWM control, in order to prevent the first element and the second element (for example, the transistors UH and UL) from being turned on at the same time, the first element is turned off immediately after turning off. Then, the second element is not turned on immediately before the next turn on. That is, it is necessary to provide a period (dead time) during which both the first element and the second element are turned off. Conventionally, when the duty ratio of the first element increases (exceeds the threshold value), the dead time cannot be ensured, so only PWM control is performed without performing complementary PWM control.

According to the first technique, the ratio (duty ratio) between the ON time and the OFF time of the first element is not changed, and the ON time is lengthened at one time (continues to be ON for several original carrier cycles in the first period), The off time is lengthened in the second period. That is, the first element is switched by average PWM control. As a result, even if the duty ratio of the first element is such a large value that the complementary PWM control cannot be performed, the off time of the first element is ensured long, and the second element can be switched by the complementary PWM control. can. That is, by performing complementary PWM control in the second period of the average PWM control period, complementary PWM control can be performed to a range in which the duty ratio of the first element is larger than in the conventional case. As a result, heat generation of the transistor can be suppressed as compared with the conventional art. Note that the duty command value is the time from the timing when the first element is turned on to the timing when the second element is turned on. As the duty ratio of the first element increases, the time from when the first element is turned on to when it is turned off increases, and the duty command value also increases. Hereinafter, control in which complementary PWM control is performed during the second period of the average PWM control period will be referred to as complementary average PWM control.

According to the second technique, the frequency of transistor switching can be reduced. The switching loss of the transistor is reduced, heat generation can be suppressed, and hunting of the current flowing through the motor can be suppressed.

According to the third technique, complementary average PWM control can be performed without excessively increasing the first period (the period during which the first element remains on). In other words, it is possible to set the shortest first period during which complementary average PWM control can be performed.

1 shows a circuit diagram of an inverter. 2 shows a timing table of an inverter when driving a motor; FIG. 4 shows a diagram illustrating complementary PWM control; FIG. 4 shows a diagram for explaining a relationship between a duty ratio and a duty command value; FIG. 10 shows a timing table in which the switching timing of the upper arm element is changed; FIG. FIG. 10 shows a timing table in which the switching timing of the upper arm element is changed; FIG. The timing at which complementary average PWM control is performed is shown. The timing at which complementary average PWM control is performed is shown. 4 shows a flowchart of control executed by the motor control device. 4 shows a flowchart of control executed by the motor control device. 4 shows a flowchart of control executed by the motor control device.

(inverter)
The inverter 100 will be described with reference to FIG. The inverter 100 is connected to the motor M and supplies the motor M with drive current. The inverter 100 has a power source 12, an inverter circuit 5 that changes the frequency of the power source 12, and a gate control that switches ON/OFF of the transistors (UH, UL, VH, VL, WH, and WL) that constitute the inverter circuit 5. It comprises a circuit 8 and a motor controller 10 which controls the gate control circuit 8 . Gate control circuit 8 and motor controller 10 are connected to power supply 12 . Although illustration is omitted, the motor control device 10 includes a CPU and a memory. Signals from a circuit for detecting the rotor position of the motor M, a circuit for detecting current flowing through the motor M, and the like are input to the motor control device 10 .

Inverter 100 is a three-phase inverter, and inverter circuit 5 includes three switching element pairs (U-phase switching element pair 6, V-phase switching element pair 4, W-phase switching element pair 2). Note that the inverter circuit 5 is sometimes called a bridge circuit. Each switching element pair 2, 4, 6 is connected to a power supply 12, and the switching element pairs 2, 4, 6 are connected in parallel. Each switching element pair 2, 4, 6 is connected in series with an upper arm element (transistors UH, VH, WH) connected to the high voltage side of the power supply 12, and connected in series with the upper arm element. It has lower arm elements (transistors UL, VL, WL) connected to .

A transistor UH and a transistor UL are connected in series, a transistor VH and a transistor VL are connected in series, and a transistor WH and a transistor WL are connected in series. Three wirings 14, 16 and 18 are connected between the upper arm element and the lower arm element. The wires 14 , 16 , 18 are connected to the terminals of the motor M. Specifically, a wiring 14 is connected to an intermediate portion between the transistor UH and the transistor UL, a wiring 16 is connected to an intermediate portion between the transistor VH and the transistor VL, and a wiring 18 is connected to an intermediate portion between the transistor WH and the transistor WL. It is connected to the. The motor control device 10 drives the motor M by switching the transistors UH, VH, WH, UL, VL, and WL to change the currents flowing through the wirings 14 , 16 , and 18 . Gates of the transistors UH, VH, WH, UL, VL, and WL are connected to the gate control circuit 8 via gate wiring (not shown).

(switching state of the inverter circuit)
The switching state of each transistor when driving the motor M will now be described with reference to FIG. The timing table 20 indicates the rotation angle (rotor phase) of the motor M and the switching state (on/off state) of each transistor. When driving the motor M, the motor control device 10 controls the gate control circuit 8 to turn on one of the upper arm elements (transistors UH, VH, WH) and turn on the selected upper arm element. One of the lower arm elements (transistors UL, VL, WL) that are not connected in series is turned on to supply current to the motor M. For example, the transistor UH and the transistor VL are on-selected for a rotation angle of 0 to 60 degrees, the transistor UH and the transistor WL are on-selected for a rotation angle of 60 to 120 degrees, and the transistor is selected for a rotation angle of 120 to 180 degrees. VH and transistor WL are selected to be on. Each transistor remains on while the motor M (rotor) rotates 120 degrees, and the combination of the upper arm element and the lower arm element changes each time the motor M rotates 60 degrees.

The motor control device 10 adjusts the rotation speed of the motor M by switching the transistor UH based on the duty ratio, for example, between 0 and 60 degrees of rotation angle. However, the transistor VL is kept on during the rotation angle of 0 to 60 degrees. Transistor UH is an example of the first element between rotation angles of 0 to 60 degrees. During the rotation angle of 60 to 360 degrees, the motor control device 10 also switches one of the two transistors selected to be on based on the duty ratio. That is, the motor control device 10 performs PWM control and adjusts the rotation speed of the motor M. FIG. In FIG. 2 , “D1” indicates a period during which a transistor switching based on a duty ratio (transistor driven by PWM control) is driven by PWM control. Any transistor with "D1" is an example of the first element in the period (rotation angle) with "D1".

The motor control device 10 further turns off a transistor (transistor UL when the rotation angle is 0 to 60 degrees) connected in series with the transistor (first element) that switches based on the duty ratio. turn on for a predetermined time. At a rotation angle of 0 to 60 degrees, the transistor UL is an example of the second element. The motor control device 10 controls each transistor to perform complementary PWM control while the motor M is being driven. In FIG. 2, the period during which the second element and the second element perform complementary PWM control at each rotation angle is indicated by "D2". Note that the motor control device 10 does not always perform complementary PWM control. Complementary PWM control and/or PWM control may not be performed depending on the duty ratio of the first element. Conditions under which the motor control device 10 performs complementary PWM control and PWM control will be described later.

(Description of complementary PWM control)
FIG. 3 shows the switching states (part of the timing table) of the transistor UH (first element) and the transistor UL (second element) at rotation angles of 0 to 60 degrees. 3A to 3C differ in the duty ratio of the transistor UH. Note that FIG. 3 shows part of the switching states of the transistors UH and UL at rotation angles of 0 to 60 degrees. Actually, the waveform shown in FIG. 3 appears repeatedly between 0 and 60 degrees of rotation. In the timing table 30 shown in (a), the transistor UH repeats the operation of being turned on for time T1 and then turned off for time T2. That is, the duty ratio of the transistor UH is "time T1/(time T1+time T2)×100%". The transistor UL is turned on after the time b0 after the transistor UH is turned off, and turned off after the time a0 (before the time b0 when the transistor UH is turned on). That is, in order to avoid a state in which the transistor UH and the transistor UL are turned on at the same time, a period (time b0) during which both are turned off is provided. Time b0 is called dead time.

In the timing table 40 shown in (b), compared with the timing table 30, the duty ratio of the transistor UH is increased to "time T11/(time T11+time T12)×100%". Note that the dead time (time b0) does not change even if the duty ratio of the transistor UH increases. Therefore, the on-time (time a1) of the transistor UL in the timing table 30 is shorter than the on-time (time a0). Note that when the duty ratio of the transistor UH increases, the time from turning on the transistor UH to turning on the transistor UL also increases. The motor control device 10 determines the timing (duty command value) to turn on the transistor UL based on the duty ratio of the transistor UH and the length of the dead time. As the duty ratio of transistor UH increases, the duty command value for transistor UL also increases. In timing tables 30 and 40, transistor UH is driven by PWM control and transistor UL is driven by complementary PWM control.

(c) In the timing table 50, the duty ratio of the transistor UH is further increased, and the OFF time (time T22) of the transistor UH is equal to or less than the dead time (time T22≦2×b0). Therefore, if the duty ratio of the transistor UH increases to "time T21/(time T21+time T22)×100%", the transistor UL cannot be turned on during the period (time T22) when the transistor UH is off. . That is, in the conventional motor control device, complementary PWM control cannot be performed when the duty ratio of the transistor UH becomes too large. However, even if the duty ratio of the transistor UH increases to "(time T21/(time T21+time T22)×100%", the motor control device 10 changes the timing table 50 and performs complementary PWM control. Control performed by the motor control device 10 when the duty ratio of the transistor UH becomes too large, as in the timing table 50, will be described.

(Control performed by motor control device 10)
Control performed by the motor control device 10 when the duty ratio of the transistor UH increases as shown in the timing table 50 will be described with reference to FIGS. 4 to 6. FIG. FIG. 4 is a portion of the timing table 50 and shows more cycle periods than FIG. 3(c). 4 to 6, in order to clearly explain the control performed by the motor control device 10, the OFF time (time T22) of the transistor UH is shown wider than it actually is. As shown in FIG. 4, the motor control device 10 determines a duty command value A1 for turning on the transistor UL based on the duty ratio and dead time of the transistor UH. However, since the duty ratio of the transistor UH is large and the duty command value A1 becomes larger than the preset threshold value, the transistor UL cannot be turned on. The "threshold" is set to a value slightly smaller than the duty command value A1 at which the transistor UL cannot be turned on.

When the duty command value A1 is greater than a preset threshold value, the motor control device 10 performs processing to change the switching timing of the transistor UH. 5 and 6 show timing tables 50a and 50b in which the switching timing of the transistor UH is changed. Note that when the duty ratio of the transistor UH is small as in the timing table 30 and the duty command value A1 is less than the set threshold value, the motor control device 10 performs complementary PWM control without changing the switching timing of the transistor UH. (see also timing table 20 in FIG. 2).

The timing table 50a shown in FIG. 5 indicates control to turn on the transistor UH twice as long as the time T21 and then turn it off twice as long as the time T22. That is, in the timing table 50a, the transistor UH is continuously turned on for two carrier cycles shown in the timing table 50 and then turned off continuously for two carrier cycles (see also FIG. 4). In other words, in the timing table 50a, the transistor UH continues to be on during the first period C1 (the transistor UH is driven at a duty ratio of 100%), and in the second period C2, the timing table 50 is kept on by the amount that was not turned off in the first period C1. Drive transistor UH with a modified duty ratio that is off longer than .

In the timing table 50a, the length of the first period C1 (the carrier cycle of the first period C1) is the same as the value of the duty command value A1. Also, the duty ratio (corrected duty ratio) of the second period C2 is (2×A1−100)%. As described above, in the control by the timing table 50a, the transistor UH is turned on continuously for two carrier cycles and then turned off continuously for two carrier cycles. The average duty ratio of the transistor UH in the total period of the second period C2 is the same as the duty ratio of the transistor UH in the timing table 50. FIG. Hereinafter, the control in which the transistor UL is driven with different duty ratios in the first period C1 and the second period C2 while maintaining the same average duty ratio as the set (original) duty ratio is referred to as complementary average PWM control. .

The timing table 50b shown in FIG. 6 shows control to turn off the transistor UH three times the time T22 after turning it on three times the time T21. In the timing table 50b, the length of the first period C1 is "2*A1" and the duty ratio of the second period C2 is (3*A1-2*100)%. Note that the motor control device 10 turns on the transistor UH n times the time T21 (n>3, n is an integer) according to the duty command value A1, and then turns it off n times the time T22. can also

As shown in FIGS. 5 and 6, in the timing tables 50a and 50b, the off time of the transistor UH in the second period C2 is longer than in the timing table 50. As shown in FIGS. Therefore, the transistor UL can be turned on while the transistor UH is off while ensuring dead time. When the duty command value A1 is greater than a preset threshold value, the motor control device 10 drives the transistor UH by average PWM control and turns on the transistor UL while securing a sufficient off period (transistor UL is controlled by complementary PWM control). drive). Control in which the lower arm element (transistor UL) is driven by complementary PWM control by driving the upper arm element (transistor UH) by average PWM control is hereinafter referred to as complementary average PWM control. Conventionally, even when the duty ratio of the transistor UH is so large that complementary PWM control cannot be performed, the motor control device 10 drives the transistor UH with average PWM control to perform complementary PWM control (complementary PWM control) on the transistor UL. It realizes driving with average PWM control).

7 and 8 show the rotation angle (rotor phase) of the motor M and the switching state (on/off state) of each transistor when complementary average PWM control is performed (timing tables 60 and 70). In the timing tables 60 and 70, "D51" indicates the period during which the transistors driven by the average PWM control are driven by the average PWM control. Also, for the transistor driven by complementary PWM control (complementary average PWM control), the period during which it is driven by complementary PWM control (complementary average PWM control) is indicated by "D52". As shown in the timing table 60 shown in FIG. 7, the motor control device 10 uses the average PWM control and the complementary average PWM control so that the duty ratio of the transistor for PWM control is small and the duty command value A1 is less than the set threshold value. Similar transistors and durations can be used to switch the transistors (compare FIG. 2).

Note that, as in the timing table 70 shown in FIG. 8, the motor control device 10 drives the transistors by average PWM control (that is, performs complementary average PWM control) and PWM control (average PWM control). Periods in which the target transistor is driven at a duty ratio of 100% (that is, periods in which PWM control is not performed) may be provided alternately. For example, at a rotation angle of 0 to 120 degrees, the period until the transistor VL, which is not driven by the average PWM control among the transistors UH and VL selected to be on, is turned off (rotation angle of 0 to 60 degrees) is the transistor UH is driven with average PWM control. The transistor UH is controlled at a duty ratio of 100% during the period from when the transistor VL is turned off until when the transistor UH is turned off (rotation angle 60 to 120 degrees). Note that the transistor VL is an example of the third element when the rotation angle is 0 to 120 degrees. Further, the transistor WL is an example of the third element at the rotation angle of 120 to 240 degrees, and the transistor UL is an example of the third element at the rotation angle of 240 to 360 degrees.

The timing table 70 repeats control for performing average PWM control every 60 degrees and control for not performing PWM control and average PWM control. Although the details will be described later, in the control such as the timing table 70, the duty ratio of the transistor selected to be ON (transistor switching based on the duty ratio) is very large (that is, the duty command value A1 is very large). ) is done when

(Arithmetic processing performed by the motor control device)
Arithmetic processing performed by the motor control device 10 will be described below with reference to FIGS. 9 and 10 and flowcharts. In the description of the flowchart, for ease of description, a period (rotation angle 0 to 0 degrees) in which the transistors selected to be ON are the transistor UH and the transistor VL will be described. 4 to 8 will also be referred to as needed.

First, the duty command value A1 is determined based on the duty ratio of the transistor UH and the dead time when complementary PWM control is performed (step S2, FIG. 4). Next, it is determined whether or not the duty command value A1 is greater than the threshold value TA1 (step S4). Note that the threshold TA1 is set based on a value smaller than the duty ratio of the transistor UH at which the complementary PWM control cannot be performed (state as shown in FIG. 3C). If the duty command value A1 is equal to or less than the threshold value TA1 (step S4: NO), the duty command value A1 is compared with a value obtained by subtracting the switching hysteresis α1 of the transistor UH from the threshold value TA1 (TA1-α1), and the duty command value A1 is obtained. is smaller than (TA1-α1) (step S12). That is, it is determined whether or not the dead time can be ensured.

If the duty command value A1 is equal to or greater than (TA1-α1) (step S12: NO), return to step S2 to determine the duty command value A1 and compare the duty command value A1 with the threshold value TA1 (step S4). On the other hand, if the duty command value A1 is less than (TA1-α1) (step S12: YES), normal complementary PWM control is performed (step S14, FIG. 2).

When the duty command value A1 is greater than the threshold value TA1, switching the transistor UH under normal PWM control fails to turn on the transistor UL (complementary PWM control cannot be performed). Therefore, if the duty command value A1 is greater than the threshold value TA1 in step S4 (step S4: YES), the process proceeds to step S6 to calculate the conditions for driving the transistor UH under average PWM control. Specifically, the duty ratio (correction duty ratio) C3 of the second period C2 is calculated (step S6).

The duty ratio C3 is calculated according to the procedure shown in FIG. First, the duty ratio C3 of the second period C2 is calculated using the formula “C3={n×A1−(n−1)}×100” shown in step S20. In the first calculation, "n=2", that is, the duty ratio C3 of the second period C2 when forming the first period C1 and the second period C2 using two carrier periods is calculated (see also FIG. 5). . Next, in step S22, the duty ratio C3 and the threshold value TA1 are compared. If the duty ratio C3 is less than or equal to the threshold value TA1 (step S22: YES), the duty ratio C3 is determined (step S26).

If the duty ratio C3 is greater than the threshold value TA1 in step S22 (step S22: NO), the process proceeds to step S24 to determine whether or not the value of "n" has reached the upper limit. That is, it is determined whether or not the number of carrier cycles used to form the first period C1 and the second period C2 has reached the preset upper limit number. If the value of "n" has not reached the upper limit (step S24: NO), the value of "n" is counted up in step S28 (that is, "1" is added to n), and the process returns to step S20. Then, the duty ratio C3 is calculated and the process of comparing the duty ratio C3 and the threshold value TA1 (step S22) is repeated until the value of "n" reaches the upper limit.

On the other hand, if the value of "n" has reached the upper limit (step S24: YES), even if the obtained duty ratio C3 is greater than the threshold value TA1 (step S22: NO), proceed to step S26, Determine the duty ratio C3. For example, when the duty ratio of the transistor UH is extremely large, even if the calculation of the duty ratio C3 is repeated, the duty ratio C3 may not become equal to or less than the threshold value TA1. Alternatively, many operations may need to be repeated until the duty ratio C3 becomes equal to or less than the threshold TA1. By setting the upper limit of "n", the load on the motor control device 10 can be reduced.

After determining the duty ratio C3, the process proceeds to step S8 to compare the determined duty ratio C3 with the threshold value TA1. If the duty ratio C3 is equal to or less than the threshold value TA1 (step S8: YES), the process proceeds to step S10, and as shown in FIG. I do). On the other hand, if the duty ratio C3 is greater than the threshold value TA1 (step S8: NO), the process proceeds to step S16, and as shown in FIG. Periods in which control is performed at a ratio of 100% (PWM control is not performed) are provided alternately. That is, when the duty ratio C3, which is a value smaller than the duty command value A1, is still larger than the threshold value TA1, in order to reduce the number of times of transistor switching, a period during which the transistor UH is switched under average PWM control and a period during which the transistor UH is switched with a duty ratio of 100 % (PWM control is not performed) periods are provided alternately every 60 degrees.

(Other embodiments)
In the flow described in FIGS. 9 and 10, the determined duty ratio C3 and the threshold value TA1 are compared, and if "C3>TA1" (step S8: NO), the period during which the transistor UH is switched under average PWM control and the transistor UH is alternately provided every 60 degrees with a duty ratio of 100%. However, as shown in FIG. 11, when "C3>TA1" (step S8: NO), normal PWM control (no complementary PWM control) may be performed.

Further, when performing the calculation for determining the duty ratio C3, without limiting the number of carrier cycles used to form the first period C1 and the second period C2 (without performing step S24), "C3 ≤ TA1" may be repeated until the duty ratio C3 is satisfied.

In the above embodiment, an example was described in which the second period (period in which the second element is driven by complementary average PWM control) is provided after the first period (period in which the first element is driven with a duty ratio of 100%). However, the first period may be provided after the second period.

Although the embodiments of the present invention have been described in detail above, they are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. In addition, the technical elements described in this specification or in the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the techniques exemplified in this specification or drawings achieve multiple purposes at the same time, and achieving one of them has technical utility in itself.

Claims (2)

A motor control device for driving a motor connected to an inverter,
The inverter has a plurality of switching element pairs in which an upper arm element connected to the high voltage side of the power supply and a lower arm element connected to the low voltage side of the power supply are connected in series,
The motor control device
performing PWM control for switching the first element of one of the upper arm element and the lower arm element selected to be ON for energizing the motor based on the duty ratio;
determining a duty command value for switching the second element so that the second element connected in series with the first element performs complementary PWM control in which the second element is turned on for a predetermined time during the off period of the first element;
Having a threshold that can ensure a dead time for preventing the first element and the second element from turning on at the same time,
the second element is capable of switching to perform complementary PWM control when the determined duty command value is equal to or less than the threshold;
Complementary PWM control is performed when the determined duty command value is equal to or less than the threshold value,
When the determined duty command value is greater than the threshold, a first period in which the first element continues to be turned on beyond the timing at which the first element should be turned off based on the duty ratio, and a first period A second period is provided in which the modified duty ratio is executed to turn off longer by the amount of time that is not turned off, and average PWM control is performed in which the average duty ratio in the total period of the first period and the second period is the same as the set duty ratio. ,
turning on the second element while the first element is off in the second period;
when the modified duty ratio is smaller than the threshold, average PWM control is performed over the entire period in which the motor is driven;
When the corrected duty ratio is equal to or greater than the threshold value, the average PWM control is performed until the third element, which is different from the first element among the upper arm element and the lower arm element selected to be ON, is turned off, and the third element is turned off. A motor control device that performs control with a duty ratio of 100% during a period from when the is turned off until the first element is turned off . The motor control device according to claim 1 ,
When setting the corrected duty ratio, the n-th corrected duty ratio of the second period when the first period spans n carrier periods is compared with the threshold, and when the n-th corrected duty ratio is greater than the threshold, , a motor control device (n≧2, n is an integer) that repeats calculating the n+1th corrected duty ratio of the second period when the first period spans n+1 carrier periods.

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